Thin-film transistors, also known as thin-film field-effect transistors or TFTs, are fabricated using new materials and processes and can be used for construction of large-scale semiconductor integrated circuits (ICs). TFTs are fabricated with various constituent thin films of an intended large-scale semiconductor IC that are deposited on a non-monocrystalline or crystalline substrate such as a glass or plastic substrate by sputtering or chemical deposition. With the development of relevant consumer electronics, there has always been the demand for larger TFT ICs incorporating more TFT units. Lithography in the manufacture of such ICs is seldom accomplishable by using a single illumination system. Steppers employed in IC fabrication and packaging usually have an illumination field of view (FOV) that is not greater than 8 inches. Although scanners use larger fields of view in the scanning direction, they are typically not greater than 10 inches. On the other hand, the manufacture of TFT ICs of the current fifth- or higher-generation requires at least a 17-inch exposure field-of-view. Therefore, the size of an illumination FOV provided by a single exposure lens lags far behind the requirements of large-area lithography. This leads to the development of projection scanners using multiple fields of view that are stitched together, which can reach good trade-offs between device size and yield in the manufacture of large-area devices and have been widely used in the fabrication of large-area semiconductor devices, flat panel displays and thin films.
However, scanning exposure using multiple objectives and multiple fields of view that are stitched together imposes even stricter requirements on the alignment system. Due to the large area to be exposed, accurate alignment requires the use of multiple alignment points. There have been disclosed an alignment measuring system and a focal plane measuring system for use in an exposure apparatus using fields of view that are stitched together. The exposure apparatus essentially includes an illumination light source, a plurality of illumination systems, a reticle, a reticle stage, a plurality of projection optical systems, the alignment measuring system, the focal plane measuring system, a light-sensitive substrate, and a substrate stage. A number of moving mirrors and laser interferometers are provided on opposing sides of the reticle. Reticle inspection systems are provided between sub-patterns on the reticle. Substrate inspection systems and adjustment systems are provided between the projection optical systems. The exposure apparatus further includes a controller. The controller is connected to all the illumination systems, all the projection optical systems, all the alignment measuring systems, all the focal plane measuring systems, all the moving mirrors, all the laser interferometers, all the reticle inspection systems, all the substrate inspection systems, all the adjustment systems, the substrate stage and the reticle stage. The reticle patterns to be exposed are divided into several exposure regions, and an alignment and scanning exposure process is performed in each exposure region. During the alignment and scanning exposure process, the reticle inspection systems, the substrate inspection systems and the adjustment systems arranged on both sides of the sub-pattern being processed are used to detect exposure parameters in order to ensure the exposure of each exposure region to be conducted in an accurate way. Additionally, the controller corrects the exposure parameters for each exposure region in order for higher exposure accuracy to be achieved. However, the conventional exposure apparatus and method suffer from the following problem: as the light-sensitive substrate typically has a certain degree of warpage resulting from heat or uneven forces during semiconductor processing, it is necessary to measure the surface profile of the substrate before the exposure and adjust focal planes based on the surface profile during the exposure, in order to eliminate the impact of the warpage. Unfortunately, in this conventional technique, the measuring focal plane of the alignment measuring systems and the measuring focal plane of the focal plane measuring systems are not the same, and it is necessary to switch between the different focal planes in order to accomplish both focal plane measurement and alignment, which will inevitably introduce errors. Thus, there is a need to invent an exposure apparatus or method capable of reducing errors arising from different focal planes of alignment and focal plane measuring systems during measurement while allowing easy operation, large-FOV lithography, a simple structure and a small footprint.